|This article is about the episode. You may be looking for the movie.|
"Heat Signature" is the twenty-fourth episode in the second season of Adventure Time. It is the fiftieth episode overall.
When Finn and Jake try to show Marceline the movie Heat Signature, she plays a prank on them by making them believe they're vampires, but it goes too far and escalates when they're manipulated by her ghost friends.
It's dusk, and Finn and Jake are visiting Marceline to show her and her friends the movie Heat Signature. When they enter her house, Marceline introduces them to her ghost friends, Wendy, Booboo, and Georgy. Finn and Jake then try to have a seat on Marceline's couch, but it is apparently very uncomfortable. Marceline says she never really uses her couch because she is always floating, so after a short session of deliberation between the two, Finn and Jake decide that they want to be turned into vampires or ghosts. Marceline agrees to turn them into vampires, but whispers to her friends that she has something even better in mind. She tells the boys to close their eyes so she can perform the Biting Ritual. Rather than biting them, she merely pinches their necks and dabs ketchup on them to simulate a bite wound. When she is done, Finn and Jake are asked how they feel; Finn says he feels the same and Jake says his neck hurts.
Marceline and the ghosts then continue their prank by making Finn and Jake think that they can suck the color red from things and turn invisible. While thinking that they're invisible, the duo tries to mess with Lumpy Space Princess, who is in the woods. However, it soon becomes apparent that the ghosts are more concerned with harming Finn and Jake when they kick the two for no reason and try to kill them by tossing them off a tower while telling them to fly. Marceline becomes angry at her friends for trying to harm Finn and Jake, but they simply ignore her and try to eat Finn and Jake's guts through their brains after they lure them to their home, 25 Blood Drive, with an invitation to a party. Marceline warns Finn and Jake of the imminent danger, but they ignore her and attend the so called party anyway, where they are almost devoured. Marceline arrives just in time, seemingly to save them, but she says that she cannot defeat the ghosts and was only there to apologize. Finn laments that they are about to die just because they wanted to be comfortable watching Heat Signature. This reminds the ghosts that they wanted to watch the movie, so they go back to Marceline's house and watch it. Finn and Jake, however, would rather be eaten than have to endure the uncomfortable furniture, but Marceline and the ghosts are so captivated by the movie that they do not even care.
- Lumpy Space Princess
- Commander and Private
- Snail (cameo)
- Melissa (off-screen)
- Lady Rainicorn (title card)
- When the ghosts take Finn and Jake for their "floating lessons," they take them to what looks like an abandoned tower with a crashed helicopter on it.
- The ghosts' chanting is actually a backmasked message to creative director Pat McHale. If played backwards, the ghosts say, "Farewell Pat. Good luck in New York. Come back soon."
- When Finn and Jake are being attacked by the ghosts, the title card music plays.
- Georgy, Wendy, and Booboo make an appearance as enemies in Finn and Jake's Epic Quest. They attack by head-butting the heroes and can turn invisible, reappearing near them.
- Finn and Jake's jiggly arms appeared for the first time since Season 1.
- Despite being aired as the twenty-sixth episode of Season 2, it appears as the twenty-fourth episode on the Complete Second Season DVD and Blu-ray, with "Mortal Folly" and "Mortal Recoil" appearing as the twenty-fifth and twenty-sixth episodes respectivley.
- The plot and title of this episode refers to the first Heat Signature film; in previous episode "Video Makers," the intended movie for the film club was the third in the series, Heat Signature 3.
- In the episode "Video Makers," Finn and Jake said they would not show any more movies that have the copyright warnings on it, but in this episode they wanted to show another movie that would have the warning on it.
- The couch in Marceline's house, which is apparently uncomfortable and hard, appears soft in "Go With Me," and neither Finn or Marceline expressed any discomfort while sitting in it.
- The tagline for Heat Signature is "Under the ocean no one can hear you die." This is similar to the tagline of the 1979 horror film Alien: "In space, no one can hear you scream."
- This episode also makes 2 references to the Iron Maiden album "Piece of Mind." Finn and Jake are rescued from falling to their certain deaths by an invisible Marceline and think they're flying (Flight of Icarus) and they almost get their brains stolen (Die With Your Boots On).
- The female ghost's name is "Wendy," a possible nod to Casper the Friendly Ghost and his best friend, a good little witch named Wendy.
- The one-faced male ghost's name is "Georgy," a possible nod to Georgie the Ghost, a character in a series of children's books by Robert Bright.
- This episode was originally titled "Blood Drive," referring to the address of the ghosts' mansion (25 Blood Drive).
- This episode was originally scheduled to air on April 25, 2011. However, due to a last minute programming change, it was replaced with a rerun of "Crystals Have Power " with the "New Episode" screen bug that day, and this episode was moved to Monday, May 9, putting it after the two-part season finale: "Mortal Folly" and "Mortal Recoil." 
- Even though it aired on May 9, a promo for the episode aired before the premiere of "Mortal Folly."